1. Field of the Invention
This invention relates to a process for producing vinegar having a high acetic acid concentration, and more particularly to a process for producing vinegar having an acetic acid concentration higher than 20 percent weight by volume in a submerged fermentation process.
In the specification and claims of this invention, the concentration of acetic acid is expressed, unless otherwise indicated, in percent weight by volume and the concentration of alcohol in percent volume by volume, and the sum of percent weight by volume of acetic acid and percent volume by volume of alcohol is called total concentration.
2. Description of the Prior Art
Hitherto, various attempts have been made for obtaining vinegar having a high acetic acid concentration. For example, in the process described in Patent Laying-open No. Sho 52-15,899 (Tokkyo Kokai Koho), vinegar having a high acetic acid concentration is obtained by a continuous batch process wherein the manner of alcohol feeding is improved and also in the processes described in Patent Laying-open Nos. Sho 52-79,092; Sho 53-41,495 and Sho 53-44,696 (Tokkyo Kokai Koho), productions of vinegar having a high acetic acid concentration are attempted by separating a multiplication tank from an acidification tank.
In acetic acid fermentation the higher the acetic acid concentration becomes, the severer the inhibition of the growth of acetic acid bacteria by acetic acid becomes the acetic acid being the main product in the acetic acid fermentation. As a result vinegar having an acetic acid concentration higher than 20 percent weight by volume has never been economically produced in a submerged fermentation process and hence there remain various matters to be improved in the acetic acid fermentation.
Also, in the case of producing vinegar by a submerged fermentation process, as the fermentation temperature is higher, the production of vinegar having a high acetic acid concentration becomes more difficult. Hromatka et al report in "Enzymologia", Vol. 15, 337-350 (1953) that in the production of vinegar by a submerged fermentation the higher the total concentration of a fermenting broth becomes, the lower the optimum temperature thereof becomes. However, the report is on the production of vinegar having an acetic acid concentration up to 12 percent weight by volume and in the reported process the growth rate of acetic acid bacteria becomes lower due to the low fermentation temperature, which results in greatly reducing the acidification rate and makes the process unpractical from an economical view point.